566 SUMMARY OF CURRENT RESEARCHES RELAi'rNG TO 



non-nucleated fragment of Asterias-owmn with Antedon-s\:)evm, the 

 result being a gastrula with no hint of Crinoid characters. The 

 argument seems to us far from convincing. That the egg-cell with its 

 relatively large amount of cytoplasm enjoys a larger potentiality than 

 the spermatozoon is evident from the facts of artificial pathenogenesis, 

 of which the author gives a very clear account, with special reference to 

 the work of Loeb, Delage and Bataillon. 



The mature ovum is a static, the" fertilized ovum a dynamic system. 

 Fertilization implies (1) the advent or formation of a centrosome (the 

 d& novo cytoplasmic origin of a centrosome is accepted as possible) ; 

 (2) the advent of a half-nucleus, restoring the quantity of chromatin to 

 the normal ; (3) the determination of sex, probably as a consequence of 

 (2) ; (4) the bringing-in of paternal characters ; and (5) a number 

 of dynamic manifestations. The essential feature in the formation of a 

 sperm-energid in the ovum is not a centrosome, but a state of the 

 cytoplasm which causes the colloids to coagulate around a centre. 

 There is a brusque change in the surface tension of the cytoplasm. 



Of great interest is Herlant's observation, in the polyspermic frog- 

 ovum, that there is a definite relation between the length of a mitotic 

 axis and the nuclear mass to be divided. An over-short mitotic axis 

 may lead to failure in cytoplasmic division, hence the importance of 

 the entrance of the spermatozoon which doubles the volume of the 

 nucleus and ensures the necessary elongation. In regard to the deter- 

 mination of sex, the author concludes that even if the ripe ovum has 

 the sex it will develop into determined by its constitution, the fertiliza^ 

 tion maintains this or changes this, according as it is effected by one or 

 other category of spermatozoon. 



According to the author, the spermatozoon does not share in the 

 " general heredity," the ensemble of causes, factors, laws in virtue of 

 which a fertilized egg gives rise to an individual of a given species, but 

 it may sliare in the " special or personal heredity" which is concerned 

 with individual parental features. The author's " heredite " corresponds 

 rather to the English " inheritance " ; it is the ensemble of all the 

 properties of the fertilized ovum. It finds its entire expression in tlie 

 physical and chemical qualities of the ovum ; but Brachet will have 

 nothing to do with any specific hereditary substances. Yet in explaining 

 the dynamic function of fertilization he has to speak of "formative 

 materials," which, along with the energids, are re-distributed and 

 stabilized in a direction determined by the meridian of the sperm's 

 entrance. 



The author's discussion of segmentation is dominated by the conclu- 

 sion that the germinal localizations existing in the egg are respected in 

 the formation of blastomeres ; they are not displaced ; they are not 

 added to ; they merely become more fixed and stable. The mosaic of 

 the egg-cell is accentuated in segmentation. 



But the image of a mosaic is not to be pressed too far. The ovum 

 is not a harlequin's dress with non-interchangeable pieces. It can 

 restore a lost fragment ; an isolated blastomere may be as good as a 

 whole ; a merotomic fragment may form a complete larva. A quanti- 

 tative change is not always followed by any serious consequence. In 



